Microbial Mineralization Research Articles

Microbial inputs at the litter layer translate climate into altered organic matter properties.

Plant litter chemistry is altered during decomposition but it remains unknown if these alterations, and thus the composition of residual litter, will change in response to climate. Selective microbial mineralization of litter components and the accumulation of microbial necromass can drive litter compositional change, but the extent to which these mechanisms respond to climate remains poorly understood. We addressed this knowledge gap by studying needle litter decomposition along a boreal forest climate transect. Specifically, we investigated how the composition and/or metabolism of the decomposer community varies with climate, and if that variation is associated with distinct modifications of litter chemistry during decomposition. We analyzed the composition of microbial phospholipid fatty acids (PLFAs) in the litter layer and measured natural abundance δ13 CPLFA values as an integrated measure of microbial metabolisms. Changes in litter chemistry and δ13 C values were measured in litterbag experiments conducted at each transect site. A warmer climate was associated with higher litter nitrogen concentrations as well as altered microbial community structure (lower fungi:bacteria ratios) and microbial metabolism (higher δ13 CPLFA ). Litter in warmer transect regions accumulated less aliphatic-C (lipids, waxes) and retained more O-alkyl-C (carbohydrates), consistent with enhanced 13 C-enrichment in residual litter, than in colder regions. These results suggest that chemical changes during litter decomposition will change with climate, driven primarily by indirect climate effects (e.g., greater nitrogen availability and decreased fungi:bacteria ratios) rather than direct temperature effects. A positive correlation between microbial biomass δ13 C values and 13 C-enrichment during decomposition suggests that change in litter chemistry is driven more by distinct microbial necromass inputs than differences in the selective removal of litter components. Our study highlights the role that microbial inputs during early litter decomposition can play in shaping surface litter contribution to soil organic matter as it responds to climate warming effects such as greater nitrogen availability.

The stoichiometric C-Fe ratio regulates glucose mineralization and stabilization via microbial processes

The association of soil organic matter (SOM) with iron (Fe) oxides by adsorption and/or co-precipitation contributes to long term C stabilization in soil. While there is an understanding of the relationship between soil carbon (C) and the biogeochemical cycling of Fe, a lack of information exists on the role of Fe oxides on the accumulation of C in paddy soils. This study aimed to assess the role of Fe (oxyhydr)oxides on mineralization and stabilization processes following amendment of paddy soil with a labile C substrate (99 atom % 13C-glucose). The study utilized 4 paddy soils with a total Fe concentration ranging from 13.7 to 55.8 g kg−1. In soils with 42.7 and 55.8 g kg−1 Fe, the addition of glucose resulted in an Fe bound organic C: Fe molar ratio (C:Fe molar ratio) ≥6, suggesting the formation of Fe-OM complexes mainly via co-precipitation. The highest portion of 13C (13.8%) protected in Fe-OM complexes was found in soil containing 55.8 g kg−1 of Fe. The stabilization of the added labile C substrate was shown, using random forest analysis, to be controlled by the C: Fe molar ratio, while substrate mineralization was regulated by the core genera Sphingomonas and Devosa (r-strategists) (affiliated to Proteobacteria) and C:N ratio. Substrate mineralization was 47% lower in soil containing 55.8 g Fe kg−1 compared to 13.7 g Fe kg−1, with a concomitant reduction in SOM priming of 37%. This reduction in substrate mineralization and the priming effect was likely due to lower C substrate availability via the formation of Fe-OM complexes, thereby protecting the C from mineralization. In conclusion, the Fe concentration in paddy soils plays a central role in the abiotic stabilization of ‘new’ C through the formation of Fe-OM complexes via co-precipitation, thereby limiting the availability of this C substrate for microbial mineralization, and at the same time modulating the microbial community structure.

Impact of natural zeolite on chemical and biochemical properties of vineyard soils

AbstractSustained tillage and continual applications of phytopharmaceutical and fertilizers using heavy machineries frequently give rise to soil erosion, loss of soil organic matter (SOM) and contamination phenomena in Mediterranean vineyards. Because of their distinctive properties, applying natural zeolites to vineyard soils can conceivably affect the efficient use of fertilizers and reduce nutrient leaching losses. This work assesses the impact of zeolite amendment at differing rates (0, 5 and 10 t/ha) on the chemical and biochemical soil properties of three vineyard soils after 6 months from initial treatments. In particular, chemical properties usually related to soil fertility were evaluated along with more sensitive indicators of soil functionality and indicators of chemical–structural characteristics of SOM. The vineyard soils amended with zeolite showed higher nutrient availability and dehydrogenase activity if compared with the control soils. In addition, even though total organic carbon (TOC) content was unchanged, a decrease in humic substances was observed in the zeolite‐treated soils. These results suggested that the stimulation of soil microbial processes by adding zeolite triggered a microbial mineralization process of soil organic carbon stocks. In addition, the modification in the chemical–structural composition of soil organic matter in zeolite‐treated soils was shown by the pyrolysis–gas chromatography (Py‐GC) results. Py‐CG of soil organic matter clearly demonstrated an increase in the labile aliphatic compound furfural and a decline in the more stable aromatic pyrolytic fragments in zeolite‐treated soils in contrast with the control soils, thus indicating the higher extent of decomposition of the SOM more stable pool.

Biogenic Fenton process – A possible mechanism for the mineralization of organic carbon in fresh waters

To explore the mechanisms that mineralize poorly bioavailable natural organic carbon (OC), we measured the mineralization of OC in two lake waters over long-term experiments (up to 623 days) at different pH and iron (Fe) levels. Both the microbial and photochemical mineralization of OC was higher at pH acidified to 4 than at the ambient pH 5 or an elevated pH 6. During 244 days, microbes mineralized up to 60% of OC in the 10-µm filtrates of lake water and more than 27% in the 1-µm filtrates indicating that large-sized microbes/grazers enhance the mineralization of OC. A reactivity continuum model indicated that the acidification stimulated the microbial mineralization of OC especially in the later (>weeks) phases of experiment when the bioavailability of OC was poor. The reactive oxygen species produced by light or microbial metabolism could have contributed to the mineralization of poorly bioavailable OC through photochemical and biogenic Fenton processes catalyzed by the indigenous Fe in lake water. When Fe was introduced to artificial lake water to the concentration found in the study lakes, it increased the densities of bacteria growing on solid phase extracted dissolved organic matter and in a larger extent at low pH 4 than at pH 5. Our results suggest that in addition to the photochemical Fenton process (photo-Fenton), microbes can transfer poorly bioavailable OC into labile forms and CO2 through extracellular Fe-catalyzed reactions (i.e., biogenic Fenton process).

Earthworms accelerate rice straw decomposition and maintenance of soil organic carbon dynamics in rice agroecosystems.

BackgroundTo promote straw degradation, we inoculated returned farmland straw with earthworms (Pheretima guillelmi). Increasing the number of earthworms may generally alter soil organic carbon (SOC) dynamics and the biological activity of agricultural soils.MethodsWe performed soil mesocosm experiments with and without earthworms to assess the decomposition and microbial mineralization of returned straw and soil enzyme activity across different time periods.ResultsWhen earthworms were present in soil, the surface residues were completely consumed during the first four weeks, but when earthworms were absent, most of the residues remained on the soil surface after 18 weeks. On day 28, the SOC content was significantly higher in the treatment where both earthworms and residue had been added. The SOC content was lower in the treatment where earthworms but no residue had been added. The organic carbon content in water-stable macroaggregates showed the same trend. During the first 14 weeks, the soil basal respiration was highest in the treatments with both residues and earthworms. From weeks 14 to 18, basal respiration was highest in the treatments with residues but without earthworms. We found a significant positive correlation between soil basal respiration and soil dissolved organic carbon content. Earthworms increased the activity of protease, invertase, urease and alkaline phosphatase enzymes, but decreased β-cellobiohydrolase, β-glucosidase and xylosidase activity, as well as significantly reducing ergosterol content.ConclusionThe primary decomposition of exogenous rice residues was mainly performed by earthworms. Over a short period of time, they converted plant carbon into soil carbon and increased SOC. The earthworms played a key role in carbon conversion and stabilization. In the absence of exogenous residues, earthworm activity accelerated the decomposition of original organic carbon in the soil, reduced SOC, and promoted carbon mineralization.

Fine root biomass stimulates microbial activity of glucose mineralization in buried humic horizon of volcanic ash soils

ABSTRACT Burial of the surface soil by volcanic ash deposition plays roles in organic matter accumulation. Assuming that decomposition of the buried humus is limited solely by labile substrate inputs, glucose inputs are hypothesized to stimulate microbial activity in buried humic horizons. We describe patterns of microbial mineralization of 14C-labeled glucose in volcanic soil profiles to test whether glucose inputs increase microbial activity similarly in the surface soil and buried humic horizons. We found that microbial biomass was dependent on fine root biomass rather than soil carbon concentration in the volcanic soil profiles. Both bacterial and fungal biomass correlated with fine root biomass. The microbial capacities of glucose mineralization in the buried humic horizons were lower than in the surface horizons. The microbial activity of glucose mineralization in the buried humic horizons is limited by (1) the smaller microbial biomass due to smaller fine root biomass and (2) the dominance of microbial community adapted to the low concentrations of substrates with low mineralization capacity. Stimulation of microbial activities in the buried humic horizons requires both fine root biomass and inputs of labile substrates.

Responses of active soil microorganisms facing to a soil biostimulant input compared to plant legacy effects

Agriculture is changing to rely on agroecological practices that take into account biodiversity, and the ecological processes occurring in soils. The use of agricultural biostimulants has emerged as a valid alternative to chemicals to indirectly sustain plant growth and productivity. Certain BS have been shown to select and stimulate plant beneficial soil microorganisms. However, there is a lack of knowledge on the effects and way of action of the biostimulants operating on soil functioning as well as on the extent and dynamic of these effects. In this study we aimed to decipher the way of action of a seaweed and amino-acids based biostimulant intended to be applied on soil crop residues to increase their microbial mineralization and the further release of nutrients. By setting-up a two-phase experiment (soil plant-growing and soil incubation), our objectives were to (1) determine the effects of the soil biostimulant over time on the active soil bacteria and fungi and the consequences on the organic carbon mineralization in bare soils, and (2) assess the biostimulant effects on soil microorganisms relatively to plant legacy effects in planted soils. We demonstrated that the soil biostimulant had a delayed effect on the active soil microorganisms and activated both plant growth promoting bacteria and saprophytes microorganisms at the medium-term of 49 days. However, the changes in the abundances of active microbial decomposers were not associated to a higher mineralization rate of organic carbon derived from soil and/or litter. The present study assessed the biostimulant beneficial effect on active soil microbial communities as similar as or even higher than the legacy effects of either A. thaliana or T. aestivum plants. We specifically showed that the biostimulant increased the active fungal richness to a higher extent than observed in soils that previously grew the two plants tested.

Efficient immobilization of Cd2+ by nanoscale carbonate hydroxyapatite synthesized by ureolytic bacteria

As one of the five most toxic heavy metals, cadmium pollution seriously endangers human health and food safety. Carbonate hydroxyapatite has attracted our attention because of its excellent cleaning ability. However, few ecofriendly synthetic processes of nanoscale carbonate hydroxyapatite limit its application. In this study, we designed a medium that was used to prepare carbonate hydroxyapatite through microbial mineralization. The nano-flaky structure gives it a large specific surface area, which not only can achieve rapid adsorption of Cd2+ but also has a large adsorption capacity (270 mg/g). Dynamic adsorption experiments showed that adsorption is a spontaneous endothermic process. Ion exchange, surface complexation, and co-precipitation are the main adsorption mechanisms. This simple and readily available bio-carbonate hydroxyapatite provides potential candidates for heavy metal bioremediation in polluted environments.

Effects of Drip Irrigation Patterns and Biochar Addition on Soil Mineral Nitrogen and Microbial Regulation of Greenhouse

Drip irrigation and biochar amendment could affect the nitrogen form and transformation. Creating a deep understanding of the interacting effects of drip irrigation patterns and biochar on soil mineral nitrogen, as well as the key functional genes and microbial community involved in nitrogen transformation is helpful for improving facility agricultural management, increasing water and nitrogen use efficiency, and reducing the nitrate accumulation and groundwater pollution caused by nitrogen leaching. Four treatments [surface drip irrigation (D), insert drip irrigation (ID, insert depth 15 cm), surface drip irrigation +10 t·hm-2 of biochar (DB), and insert drip irrigation +10 t·hm-2 of biochar (IDB)] were conducted in a solar greenhouse, and non-rhizospheric and rhizospheric soils of pepper plants were studied. There was no effect of drip irrigation patterns and biochar on ammonium-nitrogen in the non-rhizospheric and rhizospheric soils. Compared with surface drip irrigation, insert drip irrigation decreased the nitrate-nitrogen concentration in the non-rhizosphere soil (P<0.05), but biochar addition weakened the difference. Biochar addition decreased the nitrate-nitrogen concentration in the rhizosphere soil under the same drip irrigation patterns. In the D treatment, biochar significantly decreased the number of copies of AOA, AOB, and nirK genes in the non-rhizospheric soil, and AOA gene copies in the rhizospheric soil (P<0.05); however, there was an increase in the number of copies of AOB and nirK genes in the rhizospheric soil of the D and ID treatments (P<0.05). Based on the structural equation model (SEM), in the non-rhizospheric and rhizospheric soils, pH and electrical conductivity were the environmental factors with the greatest influence on the ammonium-nitrogen and nitrate concentrations, respectively, and the gene copy number of AOB was the biotic factor with the greatest influence on the nitrate-nitrogen concentration. Based on PICRUSt, the γ-Proteobacteria contributed mostly to ammonia monooxygenase gene (K10945) expression, whereas the α-Proteobacteria, especially the rhizobia members, contributed mostly to nitrite reductase gene (K00368) expression. Biochar addition regulated the bacterial community structure that participated in K10945 gene expression in the non-rhizospheric soil and K00368 gene expression in the rhizospheric soil (P<0.05). Overall, biochar addition contributed more to nitrate-nitrogen and microbial mineral nitrogen-transformation processes in the agricultural soil than did the drip irrigation patterns.

ВЛИЯНИЕ МИКРОБНОЙ КАРБОНАТНОЙ МИНЕРАЛИЗАЦИИ НА ГИДРОФОБНОСТЬ ПОВЕРХНОСТИ ЦЕМЕНТНОГО КАМНЯ

The effect of microbial carbonate mineralization on increasing the hydrophobicity of the cement stone surface is theoretically justified and experimentally confirmed. Based on experimental studies and analysis of literature data, the main stages of microbial-induced sedimentation of calcium carbonate on the surface of a cement stone are formulated. Changes in the morphology of the cement stone surface due to crystalline new formations formed during biomineralization in the postgenetic period are described. It is shown that biocolmatation of the interstitial space of a cement stone by crystalline new formations leads to an increase in hydrophobicity, as evidenced by an increase in the contact wetting angle. The relationship between the change in the concentration of calcium in neoplasms and the average value of the contact wetting angle on the surface of the cement stone from the type of bacterial culture is established. According to chemical and morphological analysis of bioinduction tumors on the surface of samples and also evaluation of changes of the contact angle compared to the original index for cement, bacterial cultures are ranked in order to increase the efficiency of use for sedimentation of calcium carbonate with their participation, as well as increase of cement materials hydrophobicity in the following sequence: Sporosarcina pasteurii  Bacillus megaterium  Lysinibacillus sphaericus  Bacillus pumilus.

Diverse drivers of long-term pCO2 increases across thirteen boreal lakes and streams

ABSTRACT Understanding the mechanisms driving carbon dioxide (CO2) concentrations in inland waters is important to foresee CO2 responses to environmental change, yet knowledge gaps persist regarding which processes are the key drivers. Here we investigated possible drivers across 13 Swedish lakes and streams where the partial pressure of CO2 (pCO2) has increased over a 21-year period. Overall, we could not identify a single dominating mechanism responsible for the observed pCO2 increase. In the 8 lakes, we found that pCO2 increased, driven either by a possible dissolved organic carbon (DOC) stimulation of microbial mineralization or by water color primary production suppression. In streams, the dominating mechanism for a pCO2 increase was either a change in the carbonate system distribution or a possible nutrient-driven decrease in primary production. This is the first study to demonstrate and explain consistent positive pCO2 temporal trends in freshwater ecosystems, and our results should be taken into account when predicting future emission of CO2 from inland waters.

Experimental strategies to measure the microbial uptake and mineralization kinetics of dissolved organic carbon in soil

Soil organic matter turnover rates are typically estimated from mass loss of the material over time or from on rates of carbon dioxide production. In the study, we investigated a new way to characterize the concentration-dependent kinetics of amino acids used by measuring microbial uptake and mineralization of 14C-alanine. We measured the depletion from soil solution after additions 14C-alanine. The microbial uptake of 14C-alanine from soil solution was concentration-dependent and kinetic analysis indicated the operation of at least three distinct alanine transport systems of differing affinities. Most of the 14C-alanine depletion from the soil solution occurred rapidly within the first 10–30 min of the incubation after 10 µM to 1 mM substrate additions. At alanine concentrations less than 250 mM, the kinetic parameters for Km and Vmax of the higher-affinity transporter were 60.0 µM and 1.32 µmol g−1 DW soil h−1, respectively. The mineralization of alanine was determined and the half-time values for the rapid mineralization process were 45 min to 1.5 h after the addition at alanine concentrations below 1 mM. The time delay after its uptake into microbial biomass suggested that alanine uptake and subsequent respiration were uncoupled pattern. The microbial N uptake rate was calculated by microbial mineralization, and an estimated Km value of 1731.7±274.6 µM and Vmax value of 486.0±38.5 µmol kg−1 DW soil h−1. This study provides an alternative approach for measuring the rate of turnover of compounds that turnover very rapidly in soil.

Study on Mechanical and Durability Properties of Desert Sand Brick Based on Microbial Mineralization

Study on Mechanical and Durability Properties of Desert Sand Brick Based on Microbial Mineralization

Biochar induced negative priming effect on soil organic carbon mineralisation by changing the microbial community structure across plant growth stages

Biochars have considerable potential to improve soil organic carbon (SOC) sequestration and consequently regulate greenhouse gas emissions. However, the important roles of microbial mediation in the biochar-induced SOC accumulation over the plant growth season have not been adequately explored. Here, we illustrated the interactive effects of biochar amendments and plant growth stages on the microbial community and SOC mineralisation. A 3-year experiment was performed in a tobacco (Nicotiana tabacum L.) field with five treatments, including no fertilisation, conventional fertilisation, and conventional fertilisation with three rates of biochar amendments. Biochar amendments significantly improved soil moisture capacity (SMC) but decreased nitrogen (N) availability. The bacterial and fungal biomasses were enriched under biochar amendments and at the rosette and vigorous stages of the crop growing season. Biochar amendments and plant growth stages substantially affected the microbial community structure, as determined by the ratios of bacteria to fungi (B/F) and Gram-positive bacteria to Gram-negative bacteria (GP/GN). Random forest modelling revealed that SMC and N availability were the important predictors of microbial community and SOC mineralisation. Structural equation modelling indicated that microbial biomass and community structure (the rations of B/F and GP/GN) were positively associated with SMC but negatively correlated with N availability. Microbial community structure was more influential than microbial biomass in reducing microbial carbon metabolism of carbohydrates (cellobiose, glucose, and xylose) and SOC mineralisation. Our study provided insights into the functional role of the microbial community in the biochar-induced negative priming effect on SOC mineralisation during the plant growth stages.

Synthesis and Characterization of Calcium Carbonate Nanoparticles via Bacterial Mineralization in Steel Slag Comprising Cementitious Materials

Bacteria-induced mineralization is a new technique to produce calcium carbonate in steel slag for the preparation of building materials. Calcium carbonate nanoparticles were precipitated as a result of the enzymatic activity of Bacillus mucilaginous subtilis in steel slag. The crystal structure and morphology of the calcium carbonate precipitate were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), while thermal properties were studied by thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The experimental results showed that the microstructure of calcium carbonate precipitate induced by the reproductive enzymes of Bacillus mucilaginous differs from the chemical precipitation in simulated pore solution of steel slag. Powder XRD patterns confirmed the formation of Bacillus mucilaginous subtilis-induced calcium carbonate with an average particle size of 42.1 nm, while the average particle size of the chemically synthesized calcium carbonate was 59.3 nm. Compared with the chemical synthesis, we found that the decomposition temperature of calcite by bacterial precipitation was higher than that for the chemically-precipitated calcite. The compressive strength improved with the amount of bacterial content. Bacterial mineralization could accelerate the rate of carbon sequestration in the mineralization process. The content of calcium carbonate in microbial mineralized steel slag increased obviously. The compressive strength of steel slag mortar with 1.5% bacterial reached up to 51.5 MPa, the compressive strength increased over 50% compared with the carbonized steel slag mortar. The micron-size calcite by bacterial mineralization resulted in a more compact structure. Our study suggests that microbial mineralization technology is a good method to utilize steel slag for building materials.

Rusty sink of rhizodeposits and associated keystone microbiomes

Iron hydroxides serve as an efficient ‘rusty sink’ promoting the stabilization of rhizodeposits into soil organic carbon (SOC). Our work aimed to understand the physicochemical and microbial mechanisms promoting rhizodeposit (rhizo-C) stabilization as influenced by goethite (α-FeOOH) or nitrogen (N), using 13C natural abundance methodologies and DNA sequencing, in the rhizosphere of maize (Zea mays L.). The addition of N fertilizer to soil increased the mineralization of both rhizo-C and SOC, while amendment with α-FeOOH decreased rhizo-C derived CO2 and lowered the rhizosphere priming effect by 0.57 and 0.74-fold, respectively, compared to the control soil. This decrease resulted from the co-precipitation of rhizo-C at the reactive α-FeOOH surfaces as Fe-organic matter complexes (FeOM), which was 10-times greater than the co-precipitation on short-range ordered minerals. The highest portion of rhizo-C (67% of the total accumulated in soil) was protected within macroaggregates (>2 mm). Carbon overlapped with α-FeOOH mainly in >2 mm aggregates, as shown by HRTEM-EDS imaging, suggesting that α-FeOOH associated rhizo-C stimulated aggregate formation. Random forest analysis confirmed that the stabilization of rhizo-C was controlled mainly by physiochemical binding within FeOM complexes and macroaggregates. Rhizo-C mineralization was regulated by the keystone microbiome: Paucimonas (β-Proteobacteria) being an r-strategist with rapid growth under soil without nutrient limitation (N treated) and Steroidobacter (Actinobacteria) with branched filaments that can access C and nutrients under oligotrophic conditions (goethite enriched soil). Two-way orthogonal partial least squares analysis revealed that the rhizosphere priming effect was facilitated mainly by the same genera, most likely due to co-metabolism. The genera belonging to Acidimicrobiaceae (Actinobacteria), Cryptococcus and Cystofilobasidium (Basidiomycota) were positively correlated with the accumulation of rhizo-C in the >2 mm aggregate size, which might due to their high affinity towards α-FeOOH and contribution to the development of aggregation via filamentary structures that interact with microaggregates. We suggest that rhizodeposit stabilization in soil was balanced by microbial mineralization and abiotic associations with the “rusty sink” and organisms with branched filaments contributing to the development of aggregation.

Pyrene biodegradation and its potential pathway involving Roseobacter clade bacteria

Microbial mineralization plays a significant role in the removal of polycyclic aromatic hydrocarbons (PAHs) from polluted environments. Bacteria affiliated to the Roseobacter clade are ubiquitous and abundant in various environments, including PAH-polluted areas. However, very little is known about the PAH degradation mechanism utilized by the Roseobacter clade. In this study, eight bacterial strains belonging to the Roseobacter clade were isolated from sediments collected from the estuary of the Pearl River. Degradation of pyrene and two other typical PAHs (phenanthrene and benzo[a]pyrene) was studied in the eight isolated strains of Roseobacter clade bacteria (RCB) and three other type strains. The results revealed that all strains had low PAH-degrading efficiency when PAHs were used as the sole source of carbon. However, upon supplementation with an alternative carbon source, the degradation was greatly stimulated. This implies that RCB degrade PAHs via a co-metabolism pathway. A putative pyrene degradation pathway in RCB was re-constructed based on genomic analysis. pahE, a functional marker gene for PAH degradation, was detected in the genomes of RCB. PAH ring-hydroxylating dioxygenase alpha subunit domain family and beta subunit domain family and PAH degradation-related Rieske [2Fe–2S] domain were also identified in the test strains. These findings provide fundamental evidence that RCB are capable of degrading PAHs through a versatile metabolic pathway.

Microbial mineralization of botryoidal laminations in the Upper Ediacaran dolostones, Western Yangtze Platform, SW China

Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era.

Changes in N supply pathways under different long-term fertilization regimes in Northeast China

Different long-term fertilization regimes probably influence N supplying capacity and N cycling processes in soils. However, the effects of fertilization regimes on the pathways of N retention and supply and the impacts of these pathways on crop N uptake remain undocumented. In this study, the contributions of different pathways to N retention and supply were investigated on the basis of a long-term experiment that began in 1990, including six treatments: no fertilizer (CK), recycled manure (M), N and P fertilizers (NP), P and K fertilizers (PK), N, P and K fertilizers (NPK), and NPK fertilizers with recycled manure (NPKM). In the maize growth season, soil microbial mineralization–immobilization turnover (MIT) was the primary driving force of N transformation under treatments without synthetic N. Conversely, NH4+ fixation and release by soil clay minerals prominently regulate N retention and supply under treatments with synthetic N. In general, soil microbial biomass N (SMBN) mineralization and fixed NH4+ release accounted for 51 % of the variation in crop N uptake and the contribution of the latter to crop N uptake was 2-fold greater than that of the former. The synchrony between crop N uptake and fixed NH4+release was higher than that between crop N uptake and SMBN mineralization. Therefore, the fixed NH4+ pool was important in synthetic N regulation at a short or medium temporal scale, especially for soils with high 2:1 clay mineral content. By contrast, MIT dominated N cycling at a long temporal scale. Clarification of the pathways of N retention and supply can provide helpful implications for optimizing N fertilizer management and enhancing the synchrony between crop N demand and soil N supply.

Patterns and Drivers of Carbon Dioxide Concentrations in Aquatic Ecosystems of the Arctic Coastal Tundra

AbstractMultiple aquatic ecosystems (pond, lake, river, lagoon, and ocean) on the Arctic Coastal Plain near Utqiaġvik, Alaska, USA, were visited to determine their relative atmospheric CO2 flux and how this may have changed over time. The nearshore coastal waters and large freshwater lakes were small sinks of atmospheric CO2, whereas smaller waterbodies were substantial sources. pCO2 was linked to dissolved organic carbon concentrations across broad spatial and temporal scales, with greater concentrations found in smaller freshwater systems (i.e., ponds and rivers). On a day‐to‐day basis, water temperatures appeared to be the strongest driver of pCO2 levels in tundra ponds, where warmer temperatures likely stimulated microbial mineralization of carbon in both aquatic and hydrologically linked terrestrial environments. Large rainfall events, which may lead to inflow of carbon‐rich groundwater into these ponds, also were associated with increased daily average pCO2. Based on comparison to historical data, we estimate that CO2 concentrations in tundra ponds have increased more than 1.8 times over the past 40 years. Quantifying CO2 flux from these abundant aquatic ecosystems on the Arctic Coastal Plain and elsewhere in the high northern latitudes will likely have important implications for furthering understanding of landscape‐level and nearshore carbon dynamics in the Arctic.